Modern electronic devices generates electromagnetic radiation with the electronic circuitry and transmission lines of the equipment. The radiation often develops as a field or as transients within the radio frequency band of the electromagnetic spectrum, i.e., between about 10 kHz and 10 GHz, and is termed “electromagnetic interference” or “EMI.” This radiation is known to interfere with the operation of other proximate electronic devices.
To mitigate EMI effects, shieldings having the capability of absorbing and/or reflecting EMI energy may be employed to confine the EMI energy within a source device and to insulate that device or other target devices from other source devices. The shielding provides a barrier that is inserted between the source and other target devices. The shield typically is an electrically conductive housing that is grounded. For electrical wire, cable, cord or other conductor, EMI shielding is often provided by enclosing the conductor within an electrically conductive conduit or housing.
A less cumbersome shielding can be accomplished by covering the wire or cable with a shielding layer woven or braided of a metal wire or other electrically conductive fibers. For example, U.S. Pat. No. 5,483,020 to Hardie et al. discloses a cable having parallel conductors surrounded by an insulating layer. The cable is then EMI shielded by a braided metal shield of a plated electrical conductor.
U.S. Pat. No. 5,477,011 Singles et al. discloses a low-noise signal transmission cable that employs an insulative layer that is bonded to a surrounding shield layer via an adhesive. The shield may be a braided metal, conductive polymer, or wrapped foil layer.
U.S. Pat. No. 5,293,001 to Gebs discloses a flexible, shielded cable assembly. The assembly includes a flexible metal conductor, a dielectric layer positioned about the conductor, and a flexible metallic shield disposed about the dielectric. The shield preferably employs a thin metallic foil and a metallic braid, ribbon, or tape disposed about the foil.
U.S. Pat. No. 5,043,530 to Davies discloses a shield cable which includes an internal conductive core with 1-4 wire leads, each of which are insulated with a wrapping of an insulative tape. The voids between the leads are filled with an amorphous elastomer. A shield layer is provided by braiding a silver-copper alloy wire over the elastomer-covered conductive core. The strands of the shield become embedded in the elastomeric material which thereby fills the spaces in the braided structure. A barrier of an insulative jacket surrounds the elastomer-covered shield and conductive core.
U.S. Pat. No. 5,015,800 Vaupotic et al., discloses a controlled impedance transmission line that consists of a flexible cable having a side-by-side pair of conductors. The conductors are surrounded by respective inner and outer dielectric layers. A braided wire shield surrounds the dielectric layers, which shield, in turn, is surrounded and penetrated by an exterior jacket.
U.S. Pat. No. 4,639,545 to Pithouse et al. discloses a conductor that is surrounded by a dielectric. A fabric in the form of a tubular sleeve is woven or positioned around the conductor. The fabric may include a conductive metal warp and a recoverable polymeric weft, which weft is recovered to secure the fabric through engagement with the dielectric.
U.S. Pat. No. 4,376,229 to Maul et al. discloses a flexible, shielded electrical conduit. The conduit includes a flexible tubing, a flexible electrical shielding disposed within the tubing, and an axially compressed, radially expanded elastic woven retainer which forces the shielding into continuous contact with the tubing. The shielding may be provided as a weave of electrically conductive filaments.
Proposals have been made to provide shielding for wires, cables, lines, and the like in the form of a tubular, heat-shrinkable outer layer within which is received a conductive inner layer. For example, U.S. Pat. No. 3,576,387 to Derby discloses a heat-shrinkable shield formed of an outer layer of a heat-shrinkable tubing having a thin layer of a metal-filled polymeric matrix bonded to the inner surface thereof. The shield may be sheathed over an insulated wire or cable, and then heated to shrink the outer layer of the shield over the insulation of the wire or cable.
U.S. Pat. No. 5,106,437 to Lau et al. discloses a conformable electromagnetic radiation suppression cover for a reflecting structure. The cover includes a tubular outer layer of an electromagnetic radiation absorber formed of a nonconductive composite with one or more kinds of dissipative particles dispersed in a shrinkable dielectric binder. An inner sealant layer is employed to fill any voids between the absorber and the structure. A thin metallic foil may be bonded between the sealant and the absorber as a ground plane.
U.S. Pat. No. 4,555,422 to Nakamura et al. discloses a magnetic shielding article that includes a heat-shrinkable outer layer of a thermoplastic polymeric material and an inner layer of a magnetic shielding layer. The shielding layer may be formed of a thermoplastic material filled with a powdered ferrite.
U.S. Pat. No. 4,915,139 to Landry et al. discloses another heat-shrinkable tubing article. Such article is formed of an outer layer of a tubular, heat-deformable material having a thermoplastic melt liner that is bonded to the inner surface thereof. A fiber reinforcement layer is disposed between the melt liner and the shrink tubing.
U.S. Pat. No. 6,005,191 to Tzeng et al. discloses a heat shrinkable jacket for EMI shielding. The jacket comprises a conductive inner layer, a thermoplastic interlayer, and a heat shrinkable outer layer. The thermoplastic interlayer bonds the conductive inner layer to the heat shrinkable outer layer when the jacket is heated. The conductive inner layer can be a nonconductive fabric and a conductive metal foil formed of copper, aluminum, or another metal, or as a combination or blend of conductive and nonconductive fibers.
A representative commercial heat-shrinkable tubing shielding is marketed under the name CHO-SHRINK® by the Chomerics Division of Parker Hannifin Corp., Woburn, Mass. The shielding is formed by coating a conductive compound onto the outer surface of a heat-shrinkable tube. Another such product is manufactured by Raychem Corp., Menlo Park, Calif., as a heat-shrinkable tube electroplated with an outer layer of a conductive metal.